1. Field of the Invention
The present invention relates to a permanent oxide magnet for use in the magnetic head-positioner in rigid disk drives or floppy disk drives which are one of the peripheries for computers. More particularly, it relates to a permanent oxide magnet coated with a thin, uniform electrodeposition layer for preventing fine magnetic particles remaining on the surface as a result of working and grinding thereof from scattering, and a method for manufacturing such a magnet.
2. Description of the Prior Art
In a magnetic head-positioner in a magnetic disk apparatus, a voice coil-type motor is used as a drive source for moving a magnetic head between tracks for writing and reading information. The coil provides linear motion, (see, for instance, Japanese Patent Publication Nos. 50-4241 and 58-35030), or rotational motion (see, for instance, Japanese Patent Publication No. 58-31662). In any case, the coil is arranged in a magnetic gap defined by a yoke and a permanent magnet, or a plurality of permanent magnets, and the coil is energized by an electric current to move according to Fleming's left-hand rule.
Widely used as a permanent magent assembled in such a voice coil-type motor is, for instance, a ferrite magnet. The ferrite magnet is produced by sintering fine ferrite particles and has fine magnetic particles remaining on the surface after working or grinding thereof, so that assembling one in the above magnetic circuit without any treatment would adversely affect magnetic recording because of the scattering of such fine magnetic particles. Accordingly, the ferrite magnet for use in the above applications is generally subjected to surface coating before being assembled in the magnetic circuit.
The coating of a ferrite magnet has been conventionally carried out by spraying a paint onto the magnet surface or dipping the magnet in a paint bath. However, spraying or dipping of paint tends to cause the sagging and accumulation of the paint in the resulting paint coating, resulting in partial unevenness in thickness. In addition, if the magnet has a complicated shape, it would have some uncoated portions, or narrow gaps thereof would be clogged by the paint.
Known generally as an alternative to these painting methods is electrodeposition coating. Among the electrodepostion coating processes, cationic electrodepositon coating is highly efficient and capable of forming a uniform coating layer, so that it has been widely used for coating of automobile bodies and parts as disclosed in Japanese Patent Laid-Open No. 58-25497.
In the cationic electrodeposition coating, the body to be coated is dipped in an aqueous paint, with the body to be coated connected to a cathode (-) and a paint tank or an electrode provided in the tank to an anode (+), and DC electric current is caused to flow between the two electrodes, causing the body to be coated to attract electrically fine paint particles to form a coating film thereon. Therefore, the body to be coated is restricted to those having good conductivity such as iron and other metals. Thus, the permanent oxide magnet having electric insulating properties has not been subjected to such electrodeposition coating.